1. Field of the Invention
The present invention relates generally to any form of hydraulic artificial lift technique including hydraulic reciprocating pumps, hydraulic jet pumps, and hydraulic coiled tubing jet pump installation and removal and, more particularly, to apparatus and methods for facilitating downhole connection, sealing, and disconnection thereof.
2. Description of the Background
While high-pressure oil formations have sufficient pressure to push production fluid to the surface, low-pressure formations typically require a downhole pump to lift the oil to the surface. Downhole pumps are of numerous types and include such pumps as sucker-rod-type reciprocating pumps as well as hydraulic-artificial-lift-type coil tubing jet pumps. The selection of the type of pump to be used depends on the particulars of the oil field. One of the big advantages of coil tubing jet pumps and similar hydraulic jet pumps is the ability to pump without moving pump components. As well, in a coil tubing jet pump installation, the numerous problems associated with a long reciprocating pump sucker rod string within the borehole running all the way from the surface to the pump are eliminated. The present invention may be used with coil tubing jet pumps or other types of hydraulic artificial lift pumps that may or may not be replacing existing sucker-rod-type reciprocating pumps. Thus, the present invention may be used with standard downhole seating nipples from preexisting pump assemblies that normally are associated with sucker-rod-type reciprocating pumps. The present invention may also be used with newly manufactured pumps and bottomhole assemblies.
For purposes of a concise explanation, only the coil-tubing-type hydraulic jet pumps are discussed herein, and it will be understood that application of the present invention is to hydraulic artificial lift techniques generally. With operation of coil tubing jet pumps, an injection fluid such as oil or water is pumped down the coil tubing string into the coil tubing jet pump at a high pressure to thereby transfer energy to the production fluid via a momentum transfer process within the throat portion of the jet pump. The momentum transfer process increases the net energy of the production fluids such that production fluids have sufficient pressure energy to push the fluids to the surface. The operation of the jet pump draws the low pressure fluid from the formation. The injection fluid and production fluids are mixed in the throat of the coil tubing jet pump and discharged into an annular space between the outside wall of the coil tubing and the inside wall of the production tubing string. The mixed fluids flow through the annulus or other pipes to the surface, where the production fluids are captured. Thus, the production fluids are induced by the jet pump to mix into the circulation path of fluids within the production string/coil tubing string annulus so as to be pumped to the surface. Typical of patented jet pumps are the pumps disclosed in U.S. Pat. Nos. 1,355,606; 1,758,376; 2,287,076; 2,826,994; 3,215,087; 3,887,008; 4,183,722; 4,293,283; 4,390,061; 4,603,735; 4,658,693; 4,790,376; and 5,083,609.
The coil tubing jet pump assembly lands in a coil tubing jet pump bottomhole assembly (BHA) that is connected to a reservoir connection, typically a sucker-rod-type reciprocating pump seating nipple, that leads to the pay zone or reservoir from which wellbore fluid, flow. Thus, the seating nipple is connected for communication with the reservoir or production zone of the wellbore. Production fluids flow from the production zone of the formation, typically through the seating nipple of sucker-rod-type pump completions, through a standing valve, as may be found in a flow path in the bottomhole assembly discussed in more detail hereinafter, and into the coil tubing jet pump. The seating nipple may typically be of the type normally used for mechanically latching onto a sucker-rod-type reciprocating pump assembly. Three typical types of such seating nipples and landing devices would include those that have a top mechanical hold-down, a bottom mechanical hold-down, and a multiple-cup hold down. Reference is made to API Standard 11-AX for typical completion components and techniques. The hold-down elements of the seating nipple and of the landing/latching device secure the reciprocating sucker-rod-type pump to the seating nipple so that the reciprocating rod pump does not ride up in the wellbore on the up stroke of the reciprocating sucker rods and provides the fluid seal necessary between fluids in the production tubing at pressure and the production fluids in the reservoir at some lower pressure.
One problem that may be encountered when using coil tubing jet pumps is the problem of making a fluid-tight connection to the seating nipple with the coil tubing jet pump bottomhole assembly. In certain situations, particularly in horizontal wellbore applications and/or in deep boreholes, or highly deviated wellbores, or wellbores that otherwise have significant frictional drag on the coil tubing, such as wells with highly viscous material therein or due to frictional drag from coil tubing to production tubing contact as may occur due to sharp turns or doglegs along the borehole, it is often difficult to drive a mechanical latching device into the seating nipple using the rather flexible coiled tubing. In fact, it is submitted that the coil tubing may bend or buckle before sufficient force is produced to latch into the API-11AX seating nipple typically installed as standard equipment. As well, mechanical latch components as used in prior art devices for latching to the seating nipple typically require significant insertion force or may become sufficiently clogged or blocked so that the small pushing force available at the bottom of the well for the BHA may not be sufficient for reliable latching. Not only must the coil tubing jet assembly be securely connected to the seating nipple, but also the connection must be fluid-tight. If the connection is not fluid-tight, then the injection fluid and production fluids discharged into the annular space at high pressure between the outside of the coil tubing and the inside wall of the production tubing string will flow through the seating nipple to thereby impede or prevent operation of the coil tubing jet pump. Thus, there is a first problem of making the seating nipple connection.
A second problem encountered is that of breaking the seating nipple connection, i.e., of releasing the downhole assembly from the seating nipple. Just as the pushing power of coil tubing at the bottom end thereof is greatly diminished in deep and/or highly deviated holes as discussed above, the pulling strength of coiled tubing at the surface is also quite limited in such situations due to the yield strength of the coil tubing in tension. The weight of all the tubing in the wellbore, plus friction force acting thereon throughout the length of the wellbore, plus any unlatching mechanism force for the seating nipple connection, plus forces such as sticking due to differential force as discussed below, or other forces, are applied to the coil tubing. Such forces sometimes cause the coil tubing to part or become mechanically damaged during attempted removal of the coil tubing, thereby possibly resulting in a costly and time-consuming fishing job.
Assuming that the seating nipple connection is fluid-tight, a differential pressure will typically be formed across the standing valve in the BHA due to a relatively low formation pressure below the standing valve as compared with a relatively high hydrostatic pressure in the coil tubing/production tubing annulus. It is submitted that this pressure differential may create a large force that must also be overcome before the coil tubing jet downhole assembly can be removed from the seating nipple. It is therefore submitted herein according to the above analysis of the problem that the load required to break the fluid seal may often be a significant portion of an imposed load on the coil tubing. In summary, as discussed above, depending on the depth and deviation of the wellbore, and other forces, the coil tubing may not have enough tensile strength at the surface to unlatch the assembly and may even part due to such forces acting thereon.
Consequently, there remains a need for an installation and removal system for coiled tubing jet pumps and artificial hydraulic lift installations generally that allows for more reliable connection, sealing, and disconnection from downhole components, such as the various types of reservoir connections, that typically comprise seating nipples. Those skilled in the art will appreciate the present invention that addresses these and other problems.